<p>Flödesfördelningen av Klarälven i den västra respektive östra älvgrenen genom Karlstad har ändrats genom åren. Flödet i den västra älvgrenen har minskat och därmed har en ökning av sedimentering skett vid inloppet. Detta medför en ökad risk för översvämningar i Klarälven och Karlstad. För att hantera detta har det föreslagits att groynes ska placeras ut uppströms Sandgrundsudden så att en jämnare flödesfördelning i de två älvgrenarna kan ske. Men att placera ut groynes medför även att vattennivån uppströms stiger vilket i sig ökar risken för översvämningar. För att undersöka hur mycket vattennivån skulle öka uppströms Sandgrundsudden har en numerisk modell av Klarälven, från bron vid Skåre ut till Vänern, byggts upp. Modellen är gjord i det endimensionella simuleringsprogrammet <em>MIKE11 </em>och beskriver de hydrauliska egenskaperna i Klarälven genom att bottentopografin samt in- och utflöden beskrivs i modellen. Under året 2003 skulle den största vattennivåökningen, strax nedströms Videholmen, vara 18 centimeter om groynes varit utplacerade. Det skulle ske vid ett flöde på 318 m³/s. Vid Skårebron skulle vattenytan stiga runt 10 centimeter. Utplaceringen av groynes skulle inte medföra översvämningar uner ett normalt år och åtgärder för flödesfördelningen i älvgrenarna måste tas för att Klarälven ska vara bättre rustad mot höga flöden.</p>

Flödesfördelningen av Klarälven i den västra respektive östra älvgrenen genom Karlstad har ändrats genom åren. Flödet i den västra älvgrenen har minskat och därmed har en ökning av sedimentering skett vid inloppet. Detta medför en ökad risk för översvämningar i Klarälven och Karlstad. För att hantera detta har det föreslagits att groynes ska placeras ut uppströms Sandgrundsudden så att en jämnare flödesfördelning i de två älvgrenarna kan ske. Men att placera ut groynes medför även att vattennivån uppströms stiger vilket i sig ökar risken för översvämningar. För att undersöka hur mycket vattennivån skulle öka uppströms Sandgrundsudden har en numerisk modell av Klarälven, från bron vid Skåre ut till Vänern, byggts upp. Modellen är gjord i det endimensionella simuleringsprogrammet MIKE11 och beskriver de hydrauliska egenskaperna i Klarälven genom att bottentopografin samt in- och utflöden beskrivs i modellen. Under året 2003 skulle den största vattennivåökningen, strax nedströms Videholmen, vara 18 centimeter om groynes varit utplacerade. Det skulle ske vid ett flöde på 318 m3/s. Vid Skårebron skulle vattenytan stiga runt 10 centimeter. Utplaceringen av groynes skulle inte medföra översvämningar uner ett normalt år och åtgärder för flödesfördelningen i älvgrenarna måste tas för att Klarälven ska vara bättre rustad mot höga flöden.

Sedimentation is one of the consequences of hydropower plant construction. Such structures not only have an influence on reservoir morphology, but also have great impact on both upstream and downstream river morphology. This study focuses on fluvial morphological changes in between two hydropower plants on the Drava River, Austria. The influence of both reservoir management methods (flushing) and human intervention (groynes) have been investigated. The first stage started with validating an unsteady Delft3D morphodynamic model of the meandering reach. This validation shows the importance of spatial grain size distribution in predicting bed load transport. Analysis of the flushing method includes investigation of the duration of gate-opening before and after peak flood. The results show that the duration of lowering the water level at the hydropower plant (by opening the gate) before starting the peak flood will not have a big influence on the river morphology upstream of the reservoir. However, the duration of maintaining the low water level after the peak flood has a large influence on both the river morphology in the upstream portion of the reservoir and on the sediment transport toward the reservoir In the second part of this study, hydraulic structural groynes were applied in the river reach. The objective was to design a groyne field that will minimize sediment transport to the reservoir. Both emerged and submerged groynes were investigated. In addition, the influences of both groyne head shape and the distribution of sediment grain size in the groyne zone were examined. This study shows that under an unsteady simulation, when the groynes are submerged by 1m at normal flow, the sediment supply to the groyne zone decreases compared to the emerged case. However, if the groynes are submerged by 0.5m, the sediment supply to the groyne zone will be greater than the emerged case for an aspect ratio in between (0.5-2). Finally, applying L-head groynes produces less erosion in the main stream and a higher sediment supply compared to straight groynes.

No / Computational Fluid Dynamics (CFD) represents a useful tool to study natural currents in the rivers and estuaries with erosive materials; therefore, it is always in the keen interest for scientists to further study and advance it, especially when numerical model has the advantages compared to actual laboratory experiment in terms of cost, time, and restrictions on conditions of the physical models and field collections. The present study deals with the hydro-morphological investigation and numerical modeling of a group of vertically stationed parallel groynes using FLOW-3D commercial software. To validate the results of the FLOW-3D simulation, it has been compared to the experiments from literature. Besides, a SSIIM 2.0 software has also been employed to compare with some of the FLOW-3D results. It was found that the accuracy of the FLOW-3D model influenced by the approach Froude number and the critical velocity ratio (Uavg/Ucr). Even though it underestimated the measured scour depth (due to complex and intense vortices, which reduce the accuracy of the numerical models), but general results from the model have reproduced the measured data well.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22049号 / 工博第4630号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 教授 藤田 正治, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Η παρούσα διπλωματική εργασία ασχολείται με την ανάλυση της τυρβώδους ροής σε ορθογωνικό, ανοικτό αγωγό τριών διαστάσεων, στον οποίον ενυπάρχουν εμπόδια της μορφής προβόλων (groynes). Τέτοιου είδους κατασκευές χρησιμοποιούνται σε πάρα πολλούς ποταμούς ώστε να διατηρείται η επιθυμητή διατομή και το επιθυμητό βάθος ροής αλλά και να αποφεύγεται η διάβρωση των οχθών σε έντονα πλημμυρικά φαινόμενα. Για την επίλυση του προβλήματος αξιοποιήθηκαν οι εξισώσεις RANS, ενώ για το κλείσιμο της τύρβης χρησιμοποιήθηκε το μοντέλο δύο εξισώσεων και το μοντέλο . Η διαχείριση της ελεύθερης επιφάνειας έγινε με την μέθοδο Volume of Fluid (VOF), ενώ η αριθμητική επίλυση βασίστηκε στην μέθοδο των πεπερασμένων όγκων και πραγματοποιήθηκε με τον εμπορικό κώδικα FLUENT 6.1.2. Για την ροή στον υπό εξέταση αγωγό θεωρήθηκε αριθμός Reynolds , ύψος τραχύτητας τοιχωμάτων και κλίση πυθμένα . Για λόγους ελέγχου της ακρίβειας της αριθμητικής μεθόδου που χρησιμοποιήθηκε, αρχικά επιλύθηκε η περίπτωση τρισδιάστατου καναλιού ορθογωνικής διατομής χωρίς προβόλους και τα αποτελέσματα που προέκυψαν συγκρίθηκαν με αναλυτικά αποτελέσματα δισδιάστατης ροής (κατακόρυφο επίπεδο) υπεράνω επίπεδου πυθμένα. Τα αποτελέσματα βρέθηκαν σε καλή συμφωνία μεταξύ τους, γεγονός που επιβεβαίωσε την καταλληλότητα της μεθόδου. Για το τρισδιάστατο πρόβλημα με τους εγκάρσιους προβόλους, η ανάλυση έδειξε ότι το διάμηκες προφίλ της ελεύθερης επιφάνειας παρουσιάζει τοπική ταπείνωση στην θέση των προβόλων, ενώ η κατανομή των διατμητικών τάσεων παρουσιάζει μια σημαντική αύξηση στο μέτωπο των προβόλων και μια μείωση κατάντη των προβόλων στον πυθμένα και στο πλαϊνό τοίχωμα συγκριτικά με τις τιμές της διατμητικής τάσης στο κανάλι χωρίς τα εμπόδια. Επιπροσθέτως, παρατηρήθηκε η δημιουργία μιας περιοχής ανακυκλοφορίας της ροής κατάντη κάθε προβόλου. Η επανακόλληση της ροής κατάντη των προβόλων υπολογίστηκε ότι συμβαίνει σε μια απόσταση 11-19 φορές το μήκος του προβόλου πλησίον του πυθμένα ενώ πλησίον της ελεύθερης επιφάνειας αυτή η απόσταση ισούται με 6-7 φορές το μήκος του προβόλου ανάλογα με τον αριθμό και την απόσταση που απέχουν οι πρόβολοι μεταξύ τους. Αξίζει να σημειωθεί επίσης ότι οι τάσεις στο πλαϊνό τοίχωμα και στον πυθμένα στην περιοχή κατάντη των προβόλων παρουσίασαν μειωμένη κατά απόλυτο τιμή συγκριτικά με την περίπτωση του καναλιού χωρίς τα εμπόδια, γεγονός που συνηγορεί στη χρησιμοποίηση των προβόλων για προστασία διάβρωσης του ακτής. / This thesis deals with the analysis of turbulent flow in rectangular, three-dimensional open channel, in which inherent cantilever barriers (groynes). Such structures are used in many rivers to maintain the desired cross section and the desired depth of flow and to avoid corrosion of the banks to intense flooding.

This thesis focused on investigating flow, coherent structures, and mechanisms leading to scour around a series of three submerged groynes in a high curvature (radius of curvature (R)/channel width (B)=1.5) channel bend using a Large Eddy Simulation Numerical (LES) model. Flow was investigated during both an initial and a later stage of scour. The results showed that the groynes appeared effective in keeping the main core of high streamwise velocity away from the outer bank wall in the region where they were installed, although high potential still existed for local scour around the groynes. During the initial stage of scour, horseshoe vortices (HVs) showed the greatest propensity to induce scour immediately upstream of the groyne tips. During the later stage of scour, the HV in front of the first upstream groyne (G1) induced very high mean pressure fluctuations on the outer bank wall. Scour was also of very great concern around the tip of G1 due to severe mean bed pressure fluctuations. Downstream of the groyne field, the presence of a counter-rotating outer bank cell was capable of endangering the stability of the outer bank. The second focus of this thesis was to investigate flow in a 135° channel bend using both Reynolds Averaged Navier Stokes (RANS) and LES numerical models. The RANS study examined the effects of curvature ratio (R/B), and aspect ratio (B/H, where H is the inlet flow depth), on secondary circulation strength, and bed shear stresses. The study revealed that a decrease in R/B was associated with an increase in secondary circulation strength and peak bed shear stress. A change in B/H also substantially affected cross stream circulation strength. The LES study was conducted in a 135° (R/B = 1.5) bend flume with a fixed bed corresponding to near equilibrium scour conditions, and the results were compared to a similar high curvature 193° bend numerical study. Inner bank vortices and shear layers were present in both cases although their characteristics were substantially different. Distributions of boundary friction velocities, and turbulence were also quite different for each case.

This thesis focused on investigating flow, coherent structures, and mechanisms leading to scour around a series of three submerged groynes in a high curvature (radius of curvature (R)/channel width (B)=1.5) channel bend using a Large Eddy Simulation Numerical (LES) model. Flow was investigated during both an initial and a later stage of scour. The results showed that the groynes appeared effective in keeping the main core of high streamwise velocity away from the outer bank wall in the region where they were installed, although high potential still existed for local scour around the groynes. During the initial stage of scour, horseshoe vortices (HVs) showed the greatest propensity to induce scour immediately upstream of the groyne tips. During the later stage of scour, the HV in front of the first upstream groyne (G1) induced very high mean pressure fluctuations on the outer bank wall. Scour was also of very great concern around the tip of G1 due to severe mean bed pressure fluctuations. Downstream of the groyne field, the presence of a counter-rotating outer bank cell was capable of endangering the stability of the outer bank. The second focus of this thesis was to investigate flow in a 135° channel bend using both Reynolds Averaged Navier Stokes (RANS) and LES numerical models. The RANS study examined the effects of curvature ratio (R/B), and aspect ratio (B/H, where H is the inlet flow depth), on secondary circulation strength, and bed shear stresses. The study revealed that a decrease in R/B was associated with an increase in secondary circulation strength and peak bed shear stress. A change in B/H also substantially affected cross stream circulation strength. The LES study was conducted in a 135° (R/B = 1.5) bend flume with a fixed bed corresponding to near equilibrium scour conditions, and the results were compared to a similar high curvature 193° bend numerical study. Inner bank vortices and shear layers were present in both cases although their characteristics were substantially different. Distributions of boundary friction velocities, and turbulence were also quite different for each case.

This thesis focused on investigating flow, coherent structures, and mechanisms leading to scour around a series of three submerged groynes in a high curvature (radius of curvature (R)/channel width (B)=1.5) channel bend using a Large Eddy Simulation Numerical (LES) model. Flow was investigated during both an initial and a later stage of scour. The results showed that the groynes appeared effective in keeping the main core of high streamwise velocity away from the outer bank wall in the region where they were installed, although high potential still existed for local scour around the groynes. During the initial stage of scour, horseshoe vortices (HVs) showed the greatest propensity to induce scour immediately upstream of the groyne tips. During the later stage of scour, the HV in front of the first upstream groyne (G1) induced very high mean pressure fluctuations on the outer bank wall. Scour was also of very great concern around the tip of G1 due to severe mean bed pressure fluctuations. Downstream of the groyne field, the presence of a counter-rotating outer bank cell was capable of endangering the stability of the outer bank. The second focus of this thesis was to investigate flow in a 135° channel bend using both Reynolds Averaged Navier Stokes (RANS) and LES numerical models. The RANS study examined the effects of curvature ratio (R/B), and aspect ratio (B/H, where H is the inlet flow depth), on secondary circulation strength, and bed shear stresses. The study revealed that a decrease in R/B was associated with an increase in secondary circulation strength and peak bed shear stress. A change in B/H also substantially affected cross stream circulation strength. The LES study was conducted in a 135° (R/B = 1.5) bend flume with a fixed bed corresponding to near equilibrium scour conditions, and the results were compared to a similar high curvature 193° bend numerical study. Inner bank vortices and shear layers were present in both cases although their characteristics were substantially different. Distributions of boundary friction velocities, and turbulence were also quite different for each case.

Cette thèse étudie l’organisation longitudinale du lit du Rhône français et son évolution depuis plus d’un siècle afin d’améliorer la gestion des sédiments du fleuve. Elle décrit d’abord la complexité géographique, géologique, et hydrologique des 512 km du système fluvial. Les extractions, l’endiguement, la chenalisation et les aménagements hydroélectriques ont simplifié le tracé latéral du chenal, incisé et pavé le fond du lit et appauvri les habitats aquatiques et riverains. La thèse caractérise ensuite plus précisément les dynamiques de fond. Elle repose sur des données bathymétriques de 1897-2010 et sur des données granulométriques issues de plus de 300 prélèvements réalisés dans le cadre de ces travaux sur l’ensemble du linéaire. Un protocole d’échantillonnage homogène a été spécialement élaboré. Les variations altimétriques du lit (zones de stockage-érosion et faciès morphologiques) et sa composition granulométrique (zones pavées ou comblées par des fines) ont été caractérisées afin d’évaluer la mobilité potentielle de la charge de fond, les apports des affluents et l’impact des ouvrages sur les conditions de transport. Il ressort 1) que l’incision du lit est principalement due à la chenalisation, 2) que les aménagements hydroélectriques ont compartimenté le continuum en provoquant le stockage de sédiments fins dans certaines retenues et en favorisant le pavage dans les vieux Rhône à l’aval de Lyon et 3) qu’une dynamique résiduelle subsiste lors de crues majeures avec une remobilisation modérée de la charge de fond. Les données des secteurs les plus pavés ont été intégrées dans un modèle hydraulique 1D permettant de quantifier la capacité de transport et le débit solide et confirmant les résultats précédents. Ces travaux permettent de formuler des recommandations de gestion durable et de restauration écologique du fleuve telles que l’ouverture des vannes de fond en crue, la modification des consignes aux barrages ou la réinjection de graviers. / This thesis studies the French Rhone riverbed longitudinal organisation and its evolution over a century, with a view to improve the management strategy for the sediments. It first describes the geographic, geologic and hydrologic peculiarities of the 512-km long fluvial system. Gravel mining, dikes construction, channelization and dams construction have simplified the lateral pattern of the channel, incised and paved the riverbed and impoverished the aquatic and riparian habitats. The thesis then more precisely characterizes the riverbed dynamics. It relies on bathymetric data collected since 1897 and on grainsize data collected specifically for this study from over 300 samples on the whole 512-km river length. An homogeneous sampling protocol was elaborated on purpose. The vertical bed evolution and grainsize distribution were analysed to assess the riverbed potential mobility, tributaries’ sediment recharge and infrastructures’ impact on sediment transport. It thus appears that 1) riverbed incision is mainly due to channelization, 2) hydroelectric dams partitioned the continuum with the accumulation of fine sediments in some backwaters and the pavement of bypassed reaches downstream of Lyon and 3) a residual dynamic persists during major floods, with moderate gravels transport. The data of paved reaches were used in a 1D hydraulic model to quantify transport capacity and bedload discharge, confirming the aforementioned results. This study helps formulate such recommendations for sustainable river management and ecological restoration as opening slush gates during floods, changing dams management instructions or reinjecting gravel.